Technical Bulletin: Sealant Paintability & Fisheye Phenomenon

The “fisheye” phenomenon, defined as small circular craters in coating surfaces, can occur with virtually every paint or coating technology and on just about any surface. Although uncommon, fisheye may even be experienced with acceptable coatings e g latex paint) on paintable sealants. Fisheye can be widespread or found in only small areas and is not identified as a sealant defect. Instead, fisheye is attributed to either the coating, contaminated surface, or application. While it may not be possible to eliminate all instances users should understand common causes of fisheye and implement prevention measures to limit occurrences. Evidence suggests that two or more coats of paint or stain are required to properly mitigate this phenomenon.

Fisheye Phenomenon Examples

The following is a noncomprehensive list of known conditions that may contribute to the occurrence of fisheye

  • Contaminated Surfaces. Silicone, oil, wax, grease, solvents or other residues may prevent uniform coating application Users should ensure all surfaces are clean and dry before application.
  • Thinners or Reducers. Watered down, or “cut back”, coatings for spraying purposes (alcohol, or other solvents) may prevent uniform coating application Excess.  thinners/reducers/water in spray lines will have a similar effect Users should follow all equipment manufacturer application recommendations.
  • Paint Sprayers. Improper pressure setting may produce sprayer “ resulting in uneven application Users should follow all equipment manufacturer application recommendations.
  • Surface Porosity. Uniform applications of some coatings, including latex paints, may be difficult on semi or nonporous surfaces (e g cured sealants) While Henkel tests a variety of paints and other coatings on its portfolio of paintable sealants, it is not feasible to test every available type Users should test a small area for acceptable coverage prior to final application.

Henkel offers several resources, including technical data sheets, for each of its sealant products.  For the most up to date information on OSI’s sealant portfolio and acceptable coating technologies, please visit our product pages for downloadable documents.


DISCLAIMER The information and recommendations contained herein are based on our research and are believed to be accurate, but no warranty, express or implied, is made or should be inferred. Henkel recommends purchasers/users should test the products to determine acceptable quality and suitability for the intended use. All adhesive/sealant applications should be tested under simulated or actual end use conditions to ensure the adhesive/sealant meets or exceeds all required project specifications. Since assembly conditions may be critical to adhesive/sealant performance, it is also recommended that testing be performed on specimens assembled under simulated or actual production conditions.